The present invention relates to a parallel type A/D analog-to-digital converter capable of operating at an extremely high speed with an extremely high degree of accuracy and with a minimum power consumption.
PCM recording systems require A/D converters capable of operating at high speed in the video band. In general, the A/D converters may be divided into the successive approximation type, the tracking type, the parallel threshold type and so on. In the parallel threshold type, a plurality of comparators each having a reference voltage corresponding to an assigned quantizing level are disposed in parallel with each other so that the analog input signal may be compared simultaneously with the reference voltages of the comparators. Therefore, the operation of the parallel threshold type A/D converter is faster than the other type A/D converters. In order for the parallel threshold type A/D converter to have a resolution of n bits, a number of (2.sup.n -1) comparators are needed, but the parallel threshold type is best adapted as a high-speed A/D converter for processing the analog input signal in the video band because the input analog signal may be simultaneously compared with all the reference voltages. However, the parallel threshold type A/D converter has a distinct disadvantage as, because of its large number of comparators, the power consumption becomes inevitably high. The present invention relates to a parallel threshold type A/D converter and a system capable of a reduction in power consumption.